var nav=document.querySelectorAll('.nav>li');
var main=document.querySelectorAll('.main>div');

for(var i=0;i<nav.length;i++){
    nav[i].index=i;
    nav[i].addEventListener('mouseover',function(){
        for(var j=0;j<nav.length;j++){
            nav[j].classList.remove('active');
            main[j].classList.remove('active');
        }
        this.classList.add('active');
        main[this.index].classList.add('active');
    });
}
